Method for preparing polymer grade low-carbon olefin through separation of methanol pyrolysis gas

Abstract

The present invention provides a method for preparing the polymer grade low-carbon olefin through separation of the methanol pyrolysis gas, including steps of the compression, impurity removal, and absorption and separation. In the absorption and separation step, the pyrolysis gas is sent to the front-end ethylene removing column, and then is, with the C4 absorbent, further absorbed and separated to produce polymer grade ethylene products, polymer grade propylene products, and C4 and C5 products. The moderate-temperature and moderate-pressure separation without a cold box according to the present invention provides safer production process, less investment in the equipment, as well as easier separation and lower energy consumption as a result of the front-end ethylene removing and C4 absorption and separation process.

Description

FIELD OF INVENTION[0001]The present invention belongs to light hydrocarbon refining technology, relating to a method for obtaining polymer grade low-carbon olefin through the separation of methanol pyrolysis gas.BACKGROUND[0002]As the important basic petrochemical raw materials, ethylene and propylene are of important symbolic significance of a country's economic development level. At present, the world's industrial production equipment of ethylene and propylene mainly adopts the steam pyrolysis of the hydrocarbons such as the naphtha and light diesel oil. In such way, the resulted pyrolysis gas is of the mixture which contains the hydrogen, methane, ethane, ethylene, propane, propylene, mixed C4 and C5, and pyrolysis gasoline, etc. and needs to be further separated and refined to produce the qualified chemicals such as the ethylene and propylene.[0003]So far there has been no industrialized device running for preparing the polymer grade low-carbon olefin through the separation of m...

AI Technical Summary

Benefits of technology

[0024]The present invention adopts the front-end ethylene removing process, in which the C4 solvent is used as the absorbent to absorb and separate the ethylene component and thus separate the polymer grade ethylene and polymer grade propylene at a low pressure, with gentle and safe operating conditions. The moderate-temperature (higher than −91° C.) separation without a cold box in the present invention provided safer production process, thus avoiding the accumulation of hazardous impurities. Meanwhile, The moderate-pressure (1.1˜2.5 MPaG) separation provides saved investment in equipment and decreases the number of the compressor's sections. Moreover, as a result of the front-end ethylene removing process, in which the ultimate refining of the ethylene is the separation from the C4 absorbent, the separation is easier with lower energy consumption.

Problems solved by technology

So far there has been no industrialized device running for preparing the polymer grade low-carbon olefin through the separation of methanol pyrolysis gas at home and abroad.

The high price of the crude oil at the international market results in the shortage of the naphtha resource.

If the conventional front-end deethanizing separation process is used for separating the MTO pyrolysis gas, high content of the propylene and propane in the MTO pyrolysis gas will result in the increased power consumption in the 5-stage compression.

This process is long and complicated, resulting in increased investment.

In the MTO pyrolysis gas, however, the gas impurities contained such as the nitrogen oxides (NOX) and oxygen will lead to the accumulation of the dangerous explosives at the location of the cold box and thus increase insecurity factors of the system.

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